Masked Disjunction — When Logic Wears a Disguise
A formal fallacy where the type of disjunction (inclusive vs. exclusive 'or') is misidentified, leading to incorrect elimination of alternatives. In natural language, 'or' is ambiguous, and treating inclusive disjunction as exclusive can invalidate reasoning.
Also known as: Inclusive/Exclusive Or Confusion
How It Works
Natural language 'or' is systematically ambiguous. People default to exclusive interpretation in many contexts where inclusive would be correct.
A Classic Example
You can have soup or salad. You chose soup, so you cannot have salad. (But the restaurant meant you could have both.)
More Examples
The job posting says candidates must have a degree in engineering or five years of work experience. The hiring manager rejects an applicant who has both, reasoning that since they have the degree, the work experience 'doesn't count' — treating an inclusive or as if it were exclusive.
A doctor tells a patient they need to reduce stress or change their diet to improve their health. The patient cuts out junk food and concludes they no longer need to address their stress levels, misreading the inclusive medical advice as an either/or choice requiring only one change.
Where You See This in the Wild
Legal contracts and policy documents where 'or' is interpreted differently by different parties.
How to Spot and Counter It
Clarify whether 'or' is meant inclusively or exclusively. Ask whether both alternatives could be true simultaneously.
The Takeaway
The Masked Disjunction is one of those reasoning errors that sounds perfectly logical at first glance. That's what makes it dangerous — it wears the costume of valid reasoning while smuggling in a broken conclusion. The best defense? Slow down and ask: does this conclusion actually follow from these premises, or am I just connecting dots that happen to be near each other?
Next time someone presents you with an argument that "just makes sense," check the structure. The feeling of logic is not the same as logic itself.